As a technique of manufacturing a wiring board of a multilayer structure (hereinafter, also referred to as a “package” for convenience), a build-up process has been widely used. In the structure of a multilayer wiring board manufactured using the build-up process, its core substrate is required to have such a thickness that the package can have stiffness. This imposes a limitation on manufacturing a thin package as a whole.
In recent years, a structure from which a core substrate is removed has been employed in order to manufacture a thinner package. The wiring board having such a structure is also called a “coreless board” meaning having no core portion. Patent document 1 (Japanese Laid-open Patent Publication No. 2007-158174) describes an example of the process of manufacturing such a coreless board. The process includes forming a pad on a temporary substrate serving as a support, sequentially forming build-up layers (insulating layers, wiring layers) on the pad and the temporary substrate, and finally removing the temporary substrate.
Such a temporary substrate has, as constituent members thereof, for example, a prepreg, metal foils (hereinafter, referred to as “inner metal foils”) respectively stacked on both surfaces of the prepreg and each having an outer size smaller than the prepreg, and metal foils (hereinafter, referred to as “outer metal foils”) respectively stacked on both surfaces of the inner metal foils and each having an outer size larger than the prepreg.
In the process for a multilayer wiring board (coreless board) using a temporary substrate, a bonded portion in an outer peripheral portion of the temporary substrate is cut out and removed, and thus the inside of the bonded portion defines a wiring formation area. Accordingly, in order to secure the largest possible wiring formation area, the inner metal foils have to be disposed with high precision, and the bonded portion has to be cut out accurately at positions corresponding to the peripheries of the inner metal foils (i.e., the bonded portion to be removed has to be minimum).
However, the state of the art is such that in the process of manufacturing a temporary substrate, effective means for positioning an inner metal foil with high precision has not yet been found.